When an electron-positron pair annihilates, the energy relea

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251.

Assertion:  It is not possible to use  35Cl  as  the fuel for fusion energy.

Reason: The binding energy of  35Cl is too small.

  • If both assertion and reason are true and reason is the correct explanation of assertion

  • If both assertion and reason are true but reason is not the correct explanation of assertion

  • If assertion is true but reason is false

  • If both assertion and reason are false


252.

Assertion: The number of electrons in a p-type silicon  semiconductor is less than the number of electrons in a pure silicon semiconductor at room temperature.

Reason: It is due to law of mass action.

  • If both assertion and reason are true and reason is the correct explanation of assertion

  • If both assertion and reason are true but reason is not the correct explanation of assertion

  • If assertion is true but reason is false

  • If both assertion and reason are false


253.

A nucleus of mass number A, originally at rest, emits on  α-particle with speed v. The daughter nucleus recoil with speed a speed 

  • 2vA + 4

  • 4vA + 4

  • 4vA - 4

  • 2vA - 4


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254.

When an electron-positron pair annihilates, the energy released is about

  • 0.8 × 10-13 J

  • 1.6 × 10-13 J

  • 3.2 × 10-13 J

  • 4.8 × 10-13 J


B.

1.6 × 10-13 J

Antiparticles of stable particles (such as the position and the antiproton) are themselves stable. However, when a particle and its antiparticle meet, the annihilation reaction can occur, the particle and antiparticle both vanish and instead two or more photons can be produced. Conservation of energy and momentum require that, neglecting the kinetic
energies of the particles, when two photons are emitted each must have an energy equal to the rest mass energy of the particles.

Thus when electron-positron pair annihilate each other, the energy released is equal to rest mass of electron and positron.

          e- + e+  → γ1 +  γ2

[  Eγ1 =  Eγ2 = 0.511 meV = 0.8 × 10-13 J ]

The total energy released = 1.6 × 10-13 J


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255.

Two parallel beams of positrons moving in the same direction will

  • repel each other

  • will not interact with each other

  • attract each other

  • be deflected normal to the plane containing the two beams


256.

Carbon dating is best suited for determining the age of fossils if their age in years is of the order of

  • 108

  • 104

  • 104

  • 106


257.

The dependence of binding energy per nucleon, BA  on the mass number A, is represented by


258.

Assertion:  90Sr from the radioactive fall out from a nuclear bomb ends up in the bones of human beings through the milk consumed by them. It causes impairment of the production of red blood cells.

Reason: The energies β-particles emitted in the decay of 90Sr damage the bone marrow.

  • If both assertion and reason are true and reason is the correct explanation of assertion

  • If both assertion and reason are but reason is not the correct explanation of assertion  

  • If asserion and reason is false

  • If both assertion and reason are false


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259.

Assertion: Energy is released in nuclear fission.

Reason: Total binding energy of the fission fragments is larger than the total binding energy of the parent nucleus.

  • If both assertion and reason are true and reason is the correct explanation of assertion

  • If both assertion and reason are true but reason is not the correct explanation of assertion

  • If assertion is true but reason is false

  • If both assertion and reason is false


260.

Assertion:  Heavy water preferred ever ordinary water as a moderator in reactors. 

Reason:  Heavy water, used for slowing down the neutrons, has lesser absorption probability
of neutrons than ordinary water.

  • If both assertion and reason are true and reason is the correct explanation of assertion

  • If both assertion and reason are true but reason is not the correct explanation of assertion

  • If assertion is true but reason is false

  • If both assertion and reason are false


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